1. Field of the Invention
This invention relates to apparatus and methods by which undesirable materials can be removed from the lower portion of a well bore, such undesirable materials including sludge, plugs, contaminated or corrosive water and sand.
2. Brief Description of the Prior Art
Sand pumps have long been used to remove sand and other solid debris from wells. Such pumps are lowered into the well on a wire line and are operated by connection of the wire line to a piston rod. The wire line is reciprocated to operate pump. Check valves are provided in the sand pumps to prevent retrograde flow back into the well during the lifting stroke of the pump. A wire line operated sand pump is limited because of the limited motion which can be imparted to the pump through the flexible wire line.
Another type of down hole tool for capturing sand, fish, propping solids and contaminated liquids is that which is described in U.S. Pat. No. 4,190,113 to Harrison. The Harrison tool is operated by a rigid string extended to a pumping device from the surface and used to impart both rotary and reciprocating movement to the tool. A pump is incorporated in the elongated string extended downwardly into well bore from the surface, and is operated by reciprocating the upper portion of the elongated string to cause liquid and solid debris to pass into the lower portion of the tool. Here the solid portion of the debris is trapped due to density difference and the liquid portion continues to move upwardly during the pumping stroke. The liquid passes through the piston, and is pumped through ports located above the piston and communicating with the annulus around the tool. In this way, the liquid is returned to the well bore after the solid debris has been separated therefrom.
The tool described in the Harrison patent is characterized by a less than optimum service life because, where corrosive liquids are pumped from the well bore, the liquid surrounds the piston rod and contacts the cylinder walls causing corrosion thereof and early weakening. Further, in returning the pumped liquid to the well bore, tha Harrison tool makes no provision for those cases where the liquid is so caustic or corrosive that it would be desirable to remove it entirely from the well by pumping it or removing it to the surface.
The Harrison tool is also susceptible to high pressure gas unloading of the debris collected in the debris retaining chamber at the lower portion of the tool. This occurs where high pressure gas is present in the well bore and develops sufficient pressure under the collected debris to force it explosively upwardly through the pump and back out of the ports which communicate the interior of the pump cylinder with the well bore. Where this occurs, the efficiency of the pump in collecting debris is obviously drastically lowered, and equally importantly, the forcing of the sand upwardly through the pump erodes the pump and valve surfaces and tends to cause fouling of the pump.
Caldwell U.S. patent application Ser. No. 342,369 describes an improved down hole tool and method of using that tool, which function effectively in the removal of either or both solid debris and corrosive liquids from the well bore, while including an effective pumping structure with a much increased operating life as compared to other similar tools. Like the Harrison tool, however, the debris removal tool described in said copending patent application includes a check valve mounted in the piston forming a part of a pump included in an elongated string which carries the tool, and such piston mounted valve is also susceptible to rapid wear due to the high velocity passage of pumped liquid upwardly in the tool. Erosion and corrosion of the valve element carried in the piston is especially pronounced where highly corrosive liquid is present in the well bore and is pumped upwardly. Further, and as compared to the present invention, where any solid particles are entrained with the liquid which passes upwardly through the hollow piston and piston rod disclosed in the copending application, a tendency exists to erode away the inlet to the hollow piston, and to damage the check valve carried therein.